Two lists of holdings are available. One for lines data, the other for levels
data. Either of these lists may be accessed by selecting "List of
Spectra" in the menu bar and then selecting the appropriate "List of
Holdings" link.

The List of Holdings for lines is arranged as a periodic table. Each element
symbol for which there are spectral lines in ASD is a link to the holdings data table
showing the following pieces of information for each stage of ionization:

Total number of spectral lines.

Number of lines with transition probabilities.

Number of lines with level designations.

Each spectrum name in the table is a link to the complete list of lines of this spectrum in ASD.
Total number of included spectral lines for all spectra of the selected element is shown at
the bottom of the table.

The List of Holdings for levels is arranged as a periodic table. Each element
symbol for which there are energy levels in ASD is a link to the holdings data table
showing the number of energy levels in ASD for each stage of ionization.
Each spectrum name in the table is a link to the complete list of energy levels of this spectrum in ASD.
Total number of included energy levels for all spectra of the selected element is shown at
the bottom of the table.

I. What Data Sources are included in ASD?

Our basic policy is to include in ASD only those atomic data which have been
critically evaluated by NIST. The main exceptions to this are the energy level
data compiled by R.L. Kelly. His data are included in ASD for a few
spectra. While the Kelly energy level lists are unpublished, many of the data contained
in them are included in his lines compilations, which have been published in
the Journal of Physical and Chemical Reference Data, under the auspices of NIST
(formerly NBS) and AIP. Still, they have not been critically evaluated by NIST,
and a disclaimer to this effect appears when energy level data for these
spectra are queried in ASD.

The advantage of this NIST-evaluated-only policy is that it affords a set of
quality reference data. The disadvantage is that critical compilations
inevitably lag behind the generation of new data. Hopefully, computerized
handling of electronic data will cut this lag substantially in the future,
but the increasing amounts of data and decreasing number of personnel are
likely to ensure that the lag will remain significant.

We note that the large majority of the older data has held up well in
comparisons with newer results, at least in the sense that the original
estimated accuracies have generally proven to be representative.

If you have reason to believe that any ASD value is incorrect, please send your
comments via E-mail to Feedback.
It would be helpful if the message included a copy of all the text contained in
the URL for the specific search. Our apologies to authors who have produced new
and/or improved values which are not yet included in ASD because critical NIST
compilations have not been performed for that spectrum since publication of the
new data.

II. Reasons for differences between NIST published and ASD values

There are several reasons why differences sometimes occur between quantities
published in NIST compilations and the NIST ASD database:

Factors that can affect energy-level and transition data:

Some values have been corrected or updated since publication. Also, some
additional entries have been made since publication.

Differences can of course also result from errors, either in the originally
published value or in the value given in ASD. If you have reason to believe
that an ASD value is incorrect, please sent your comments via E-mail to
Feedback. It would be helpful if
the message included a copy of all the text contained in the URL for the
specific search.

Factors that can affect transition data only:

The data integration process for lines takes data from the most recently
compiled data source for each line. For example, only the transition
probabilities themselves are taken from the published transition probability
compilations. All the information for the lower and upper levels of each
transition are taken from the most current NIST compilations of energy levels
for the appropriate spectrum. The Ritz wavelengths are derived from these
level energies. Even the transition probabilities themselves may differ from
those in the older compilations, because the values from the most recent NIST
compilations are used when available.

The user may request to display both the observed and Ritz wavelength,
the latter being derived from the difference in level energies. Both observed
and Ritz values are only available for spectra for which comprehensive line
lists are included. For some spectra, only a single wavelength, observed or
Ritz, is available, in.which case the other value will be blank in the output.
When both the upper and lower level energies are available, the Ritz
wavelength is available. If both the observed and Ritz wavelengths are
available, the "Obs-Ritz" difference is also available and can be
included in the output.

Small differences for wavelengths, λ, may also result from our uniform application of a) an
algorithm for determining the significant figures in Ritz wavelengths,
and b) the index of refraction in air. This can in turn result in small
changes in the transition probabilities, which, for electric-dipole-allowed
transitions, are proportional to λ-3, and oscillator
strengths, which are proportional to λ-1.

Except for the home page, all pages of the database contain a menu bar at the
top, which may be used to navigate to any portion of the database mentioned
above. For example, if the user is viewing the Levels Form and wishes to now
view the Lines Form, the words "Lines Form" in the menu bar may be
selected to access the Lines Form. If the user is viewing the Lines Form and
desires help, the word "Help" in the menu bar can be selected to
access the ASD Help page.

The ASD home page provides links for the user to access the
following home pages and databases:

The ASD database provides two primary search forms for accessing
data. The Lines Search Form (referred to
as the Lines Form) provides access
to transition data for atoms and atomic ions (referred to as lines data).
The Energy Levels Search Form (referred to
as the Levels Form) provides access to
energy levels data for atoms and ions (referred to as levels data).
These forms require that the user fill in the spectrum/spectra of interest
(and for lines queries the wavelength region of interest)
and then select the "Retrieve Data" button.
Access to output options
(e.g., selection of HTML tabular output or ASCII output) and additional search
criteria (e.g., selection of an energy bound) is provided.

The ASD database provides the user with the option to view data as either an
HTML formatted table (which includes subscripts and superscripts) or as an
ASCII table. The default is to display the output as an HTML formatted table.

The ASD database provides the user with the option to view data either in its
entirety or in pages. The default is to display the output in its entirety,
i.e., as one output file that can be scrolled through.

By increasing the window size and decreasing the font size, it is possible to
view more data per screen.

Viewing Data as an ASCII Table

An advantage of viewing ASCII output is that it takes less time
to display ASCII output than formatted data. Another advantage is
that ASCII data may be downloaded into a spreadsheet or other program
located on the client computer.
Both the Lines Form and the Levels Form, have a section for
"Output Options".
Under the "Output Options" section, next to the "Format output"
heading, the pull down menu can be used to select "ASCII (TEXT)".

Viewing Pages of Data

An advantage of viewing data one page at a time is that the column headings
are displayed at the top of each page of data.
Another advantage is that viewing smaller amounts of data is much faster
than viewing a large file of data in its entirety. A disadvantage of viewing
data one page at a time is that it may be more convenient to scroll through
one large file of data instead of waiting for the browser to load the next or
previous page.

Each page of data includes the current page number, the total number of
pages, and links to view the next page of data or the previous page of data.
The page size can be customized to accommodate variance in font size and screen
size.

To change the default so that output is displayed in pages that can be viewed
one at a time, follow the steps listed below.

From either the Lines Form or the Levels Form, look for the section
labeled "Output Options".

Under the "Output Options" section, next to the "Display output"
heading, use the pull down menu to select "in pages."

The page size can be changed as needed.

Viewing Large Amounts of Data

The default is to display output as an HTML formatted table
in its entirety. There is a certain amount of overhead associated
with creating output containing a large number of lines of
data formatted as an HTML table. The speed with which search
results can be viewed by the user is a function of the following:

the speed of the client computer,

the amount of memory on the client computer,

the amount of data,

the number of columns of formatted output,

the speed of the network, and

the browser's ability to load and render formatted tables.

Note that in some cases, for searches returning a large amount of
output, some browsers may lock up or not
be able to display all the data correctly. If you have a problem
viewing a formatted table of data, choose one of the other display
options or limit the range of your search.

An advantage of displaying all lines of output as a formatted table is
that the user is able to view the formatted data in its entirety. Another
advantage is that the user can use the browser's "find" capability
to scroll down to a value of interest. The disadvantage is that this option
can be very slow. A considerable amount of time will need to be spent loading
the data into the browser, and having the browser determine how to render the
many columns of data.

Users with less capable systems, or users primarily interested in viewing the
first portion of the data, may opt to choose one of the following options:

Display 100 lines (maximum page size) as a formatted table.
Two advantages of this option are that it is faster than viewing the formatted
data in its entirety and that the user is still able to view a large portion of
the data (100 lines) at a time. Another advantage is that the user is able to
see column headings displayed at the top of each page of data. The disadvantage
is that the user is not able to view the data in its entirety.

Display 15 lines (or default page size) as a formatted table.
The advantages of this option are that it is relatively fast and that the user
is able to view formatted data. Another advantage is that the user is able to
see column headings displayed at the top of each page of data. The disadvantage
is that the user must view pages of data one by one.

Display output as an ASCII table.
This option has the advantage that it is relatively fast. The browser does not
need to load a large file containing formatted data and the browser does not
need to spend time determining how to lay out the many columns of data. Another
advantage is that the user can scroll through the data in its entirety. The
disadvantage of this option is that the user is not able to view superscripts,
subscripts, italics, etc. that can be viewed with formatted data.

In a text editor, remove any undesired headers from the saved ASCII
output file, and

When reading the ASCII output file into spreadsheet software, specify the
delimiter as a pipe, i.e., "|".

Changing Fonts

Font size effects the amount of data that can be viewed per screen;
a smaller font size allows more data to fit on each screen.

Finding Specific Values in Output

WWW browsers provide the capability to find specific words/patterns in
a page of output displayed. For example, using an HTML page of output
for Lines Data or Levels Data, if the user searches for "5/2"
then the browser will scroll down to the line of data containing the value
specified and highlight the value.

Because of the way data are formatted,
care must be taken when searching for values. Note the following examples.

To search for the configuration "2s22p2"

for ASCII output: Search for the phrase "2s2.2p2 ." Note that periods are
inserted whenever necessary to avoid ambiguity due to the lack of superscripts.
Angular brackets enclose J values of the parent terms.

HTML Table: Search for the phrase "2s22p2".

To search for the term "3D" note that it is easier to specify a case sensitive search.

To search for the term "2[5/2]:"

ASCII output or HTML Table: Search for the phrase "2[5/2]."

To search for the J value "3/2,5/2":

ASCII output or HTML Table: Search for the phrase "3/2,5/2."

To search for the energy level "60333.43:"

ASCII output: Search for "60333.43".

HTML Table: Search for "60 333.43"

To search for the energy level "87789.63:"

ASCII output: Search for "87789.63."

HTML Table: Search for "87789.63." Note that
searching for "87789" will not work. To search for all energy
levels greater than 87000, search for "87".

Printing Data

Many WWW browsers offer the capability to print directly from the browser. An
alternative is to download the data and then print the data from the local
computer.

The database provides an option which allows a user to choose the columns of
data to display. Suppressing specific columns of data might be helpful for
printing purposes. Specifying landscape orientation and reducing the font size
will simplify the task of printing a large amount of data.

The number of equivalent electrons (occupation number for a particular
subshell) is given as a full-size integer following the electron symbol
(e.g. 4d5 represents 4d5). The symbols for different
subshells not separated by parent terms or spaces are separated by periods
(e.g. 4f3.5d.6s2 represents 4f35d6s2). The
multiplicity of a term is given immediately preceding the term symbol,
and an odd-parity term is indicated by an asterisk following
the term symbol (e.g. 3H* represents
3H°). The parity of a level
having no term name is also indicated by the presence (odd parity) or absence
(even parity) of an asterisk in the "Term" column. The J value
of a level given with a configuration designation appears within "< >"
brackets following the term symbol (e.g. 2s2.2p4.(3P<2>).3d
represents
2s22p4(3P2)3d
and (3p5.(2P*<3/2>).5g represents
3p5(2P°3/2)5g).

The bibliographic references given in ASD are HTML links to complete
bibliographic records stored in the NIST Atomic Spectra Bibliographic
Databases. ASD is integrated with two of these Databases, Atomic Energy
Levels and Spectra Bibliographic Database and Atomic Transition
Probability Bibliographic Database. The complete bibliographic records
are displayed in a separate new window and contain, where available, HTML
links to online journal pages hosting the articles. If the user has a
subscription to the online journal, it is possible to download the full-text
article from the journal.